1. Field of Technology
The present invention relates to hydraulic systems. More particularly, it relates to the selective activation of a powered mode and/or a gravity mode for lowering a lift gate.
2. Discussion of Related Art
In a typical configuration, many hydraulic lift gate systems operate in a gravity down mode. “Gravity down” means that the force of gravity drives the lift gate from one position to another. For example, the lift gate platform may be driven by the force of gravity from a first upper position to a second lower position. The present disclosure, however, is not limited to this particular example. Any change in configuration of lift gate components that is driven by gravity, e.g., movement of the platform from a folded to an unfolded configuration, is considered a gravity down mode for the purposes of the present disclosure.
The gravity down mode consumes the least amount of energy as the weight of the gate lowers the platform to the ground. With light platforms and/or in cold weather, however, there can be problems with the platform lowering to the ground or traveling to the ground too slowly. Also, as the hydraulic oil becomes more viscous in cold temperatures, it will move more slowly through the system in the gravity down mode. This creates a problem for truck fleets operating in seasonal climates, as the fleet operator may have to incur the expense of changing the oil in the hydraulic lift system to a different viscosity depending on the season.
A conventional solution for customers with this issue is to purchase, at a higher price, a hydraulic liftgate system that applies hydraulic power both to raise and lower the platform. The use of hydraulic power to lower a platform is referred to as a “power down”. The disadvantage of this alternate system is that the customer will not enjoy the benefits of energy savings of operating in a gravity down mode when power down is not necessary.
Other customers that do not operate in cold weather, may still benefit from a power down mode in certain circumstances. For example, the load on the platform increases the speed at which the lift gate platform lowers and a power down mode may not be needed depending on the weight of the load. However, when lowering an empty platform, particularly an aluminum or other lightweight construction platform, the driver may want a power down mode to speed up the lowering of the platform to save time.
As noted above, the power down system requires more components and consumes more energy, thereby using more battery power. Experience has taught that some customers can have an issue with the batteries running out of power before finishing their route. Thus, conserving battery power is an important issue, particularly for fleet operators with many stops and short routes. Accordingly, a system is needed that provides the option of a power down mode of operation when needed, but which also enables the conservation of battery power when it is determined that it is not needed.